Atkins — Factors affecting Hydrogen Ion Concentration of Soil. 401 



that numerous patches or groups of the plant occur ; and plentiful that 

 numerous isolated plants are found. 



Ulex eurojMeus is widely distributed, but its occurrence is mainly in the 

 acid region. Thus, out of twenty-seven situations, five were from pH 5'4 

 to under pH 6, sixteen were from pH 6-7, two pH 7-8^ and four pH 8-8-6. 

 Of those beyond pli 7, only one at pH 7'2 was an abundant situation, and 

 two were single bushes only. The remaining three were situations with a 

 number of isolated bushes. It is plentiful on soil above limestone around 

 Cork Harbour, but no opportunity of examining these regions has arisen. 

 It is possible that the soil is boulder clay not derived from the limestone. 



Suius fruticosus must be placed among plants with a wide range, 

 having been found between pH 5-4 and 8'4, being distributed abundantly 

 through the whole of it. However, Briggs (1880) records thirty-eifht 

 sub-species in his Flora of Plymouth, and twenty-two are recognized by 

 Hooker (3rd ed., 1884), not including B. scixatilis, which is given as a species. 

 It is probable that a study of the varieties would show a less extended range. 



The foregoing outline may be amplified by reference to the alphabetical 

 list of plants in Table II, which records the pH limits. It is hoped that both 

 species and situations may in the future be examined in greater number. 



So far no reference has been made to the reaction of the soil carrying 



crops, since their occurrence is directed, and not natural. It is, however, a 



subject of much importance. One can instance the work already mentioned 



on the occurrence of potato scab ; a paper accompanying this points out a 



relation with the " finger and toe " disease of turnips and other Cruciferae. 



It will be of interest to see whether many of this group are unable to thrive 



in soil even slightly acid ; the majority are recorded by Briggs as occurring in 



localities known to the writer to have predominantly alkaline reactions, 



many exclusively so. If an alkaline region is acid in any part, this is either 



a boggy spot or a steep bank from which bicarbonate is readily leached out. 



Since it is laborious and costly to alter the reaction of the soil to suit the 



crop, the alternative is to choose the crop to suit the soil reaction, and this 



is being done to a considerable extent in Sweden, Germany, Austria, and the 



United States, where, in Minnesota, for example, as described by Alway 



(1920, 1 & 2), peaty soils are being brought into cultivation by supplying 



their deficiency in phosphates and sometimes in potassium, the crops most 



commonly grown being grasses for hay, onions, celery, lettuce, potatoes, beets, 



etc. The subject is undoubtedly worthy of greater attention in Ireland, as 



such large areas of peaty land occur. As mentioned previously, an acid 



peaty soil differs in important respects from a clay soil of equal hydrogen ion 



content. 



SCIENT. PECO. R.D.S., VOL. XVI, NO. XXX. . 2 Z 



